To be acceptable, processes for manufacturing cannula assemblies, which include a hub and cannula, must satisfy several requirements. For example, the process must have a low incidence of damaging the point of the cannula. Second, the process must have a low incidence of plugging the hollow passageway extending the length of the cannula. Third, the hub must hold onto the needle notwithstanding a film of lubricant such as silicone located on the needle. As will be appreciated, the film of lubricant is placed on the needle to reduce the resistance of skin to puncture by the needle. Fourth, the process must provide a cannula assembly in which the minimum force required to push the cannula out of the hub is greater than forces associated with its intended use, thereby precluding disassociation of the cannula from the hub.
The standard manufacturing process for cannula assemblies to be used in medical applications typically includes numerous steps. In a first step, the blunt end of the cannula is subjected to a grit blast to provide a roughened surface. A suitable epoxy is applied to the roughened surface, and the roughened surface is then placed into a cylindrical passage in a hub. The cylindrical passage has a number of peripherally disposed channels to contain the epoxy. The narrower sections of the passage (disposed between the peripheral channels) typically have a radius larger than that of the roughened surface of the cannula. The roughened surface permits the epoxy to form a strong bond between the peripherally disposed channels of the hub passage and the roughened end of the cannula. The epoxy is than cured by a suitable process, such as by exposure to ultraviolet light, elevated temperatures (via radiant heating or induction heating), and the like. Alternatively, the epoxy can use a one stage curing process with air curing or a two stage curing process in which the epoxy is mixed with a hardener or other reactant to cause curing of the epoxy. In another process, the hub is injection molded when the roughened surface is in the mold. Further, detail on conventional manufacturing processes is contained in U.S. Pat. Nos. 4,581,024; 4,655,764; 5,026,355; 5,215,621; and 5,207,853, each of which is incorporated herein by this reference.
These processes can have a number of drawbacks. First, there can be incompatability with the epoxies used to secure the cannula to the hub and the plastic material in the hub. Second, the need to cure some adhesives using ultraviolet curing requires a hub that is substantially transparent. This requirement imposes further substantial limitations on the types of plastics that can be used to form the hub. The use of a thermal cure of the adhesive can cause physical or chemical changes of the plastic which can undesirably alter the physical characteristics (e.g., strength) of the material. In addition, all the above processes require extra time in to manufacture a cannula assembly, which significantly increases costs.